Background: Cranial bone defects are often left following brain surgery, usually to allow swelling of the brain to recover before subsequently re-implanting a protective covering of the brain at a later time (cranioplasty). These procedures are performed anywhere over the cranial vault, either unilaterally or bilaterally. The original piece of bone (autologous bone plate = bone flap) is placed in a sterile container and stored in a refrigerator at temperature of -40oC.